A GPSS model is developed for simulating air traffic flow at a major metropolitan airport. It simulates scheduled and non-scheduled flights and incorporates official airline guide flight schedules, Department of Transportation delay statistics, and additional data obtained from all airlines operating out of Detroit Metropolitan Wayne County Airport. Simulation outputs include capacity and delay statistics which can be tabulated by runway, gate, and air carrier. This model can be used to study the effect of weather conditions, scheduling patterns, and runway utilization modes on airport congestion and flight delays